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"There is no consensus ... as to why it happened," the study says of declines

Still, America has a higher rate of homicide than any other developed nation

Gun-related homicides and crime are "strikingly" down from 20 years ago, despite the American public's belief that firearm crime is on the upswing, a new study said Wednesday.

Looking back 50 years, a Pew Research Center study found U.S. gun homicides rose in the 1960s, gained in the 1970s, peaked in the 1980s and the early 1990s, and then plunged and leveled out the past 20 years.

"Despite national attention to the issue of firearm violence, most Americans are unaware that gun crime is lower today than it was two decades ago," the researchers say.

A Pew survey of Americans in March found 56% believed gun-related crime is higher than 20 years ago and only 12% said it's lower. The survey said 26% believed it stayed the same and 6% didn't know.

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The new study found U.S. firearm homicides peaked in 1993 at 7.0 deaths per 100,000 people. But by 2010, the rate was 49% lower, and firearm-related violence -- assaults, robberies, sex crimes -- was 75% lower in 2011 than in 1993, the study found.

Those drops parallel an overall decline in violent non-fatal crime, with or without a gun, the study said.

In fact, gun-related homicide rates in the late 2000s were "equal to those not seen since the early 1960s," the study found.

Explanations for the drops the past 20 years aren't clear, the study said.

"Researchers have studied the decline in firearm crime and violent crime for many years, and though there are theories to explain the decline, there is no consensus among those who study the issue as to why it happened," the researchers say in a summary.

Despite the decline, the United States still has a higher rate of homicide than other developed countries, the study says. But America doesn't have a higher rate for all other crimes.

The United States also has a higher rate of gun ownership than any other developed country, the study said.